Speaker synchronization technique for wireless multichannel sound data transmission system

ABSTRACT

The present invention relates to sound data transmission between a wireless sound transmitter that transmits sound data received from a multimedia source, and a wireless sound speaker that outputs sound signal by receiving the sound data, and more particularly, to a method for compensation of a replay time delay between the wireless sound speakers occurring when the multichannel sound data is distributed and transmitted from the wireless sound transmitter to the multiple wireless sound speakers. The differences in the replay time points occurring between the speakers in a TDMA based multichannel wireless transmission system, are pre-compensated through the delay of the sound data in the WSDT.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2009-0122590, filed on Dec. 10, 2009, and Korean Patent Application No. 10-2009-0123359 filed on Dec. 11, 2009, in the Korean Intellectual Property Office, the entire disclosures of which are incorporated herein by reference for all purposes.

BACKGROUND

1. Field

The following description relates to data transmission between a wireless sound transmitter and a wireless sound speaker that outputs, and more particularly, to a method for compensation of a replay time delay between the wireless sound speakers that occurs when the multichannel sound data is distributed and transmitted from the wireless sound transmitter to the multiple wireless sound speakers.

2. Background

Home theaters are vastly popular in the home environment. The term ‘home theater’ was used before the digital versatile disks (DVD) were commonly used, but it has been generalized after DVD systems became more widely used. A DVD system provides an excellent picture quality and a realistic sound for a user.

DVD has an advantage in that it can provide an exceptionally realistic sound compared to that of a laser disk (LD), a video home system (VHS), or a video compact disk (VCD). For example, in a scene from the movie ‘Saving Private Ryan,’ when a bullet is flying forward from behind, the sound replayed by the speaker system in the theater actually moves forward from behind simulating the direction of the bullet. In the movie ‘Matrix,’ when a helicopter is hovering above the head of the actor, the sound replayed by the speaker system in the theater makes viewers feel as if the helicopter is really hovering above their heads. Such three dimensional sound effect may be realized by multichannel digital sound technology. The most commonly used multichannel digital sound nowadays is digital multi-channel sound, for example, 5.1-channel digital sound or 6-channel digital sound.

5.1-channel is comprised of five channels including left and the right front channels located in front of a user, left and the right rear channels located in rear of the user, a center channel, and a 0.1-channel subwoofer that enhances a low frequency region. The speakers for the front channels that are located in front of the viewers are called main speakers. The role of the main speakers is to cover the background music and sound effect connecting the left and the right directions in front of the listeners.

Typically, larger speakers are used as the main speakers as compared to the other speakers because they are advantageous when replaying the stereo channels, but the main speakers are not necessarily larger than the other speakers. A speaker for the center channel, called a center speaker, covers dialogue and the human voice, i.e. vocal sounds, and it delivers a certain level of music and/or sound effects to the listeners. Occasionally, the center speakers are installed above the television so that the sounds are heard as if the actor on the screen are talking to the viewers. The speakers for the rear channel are called rear speakers or surround speakers and are usually installed at the both sides of the rear area of the listeners. The rear speakers mainly cover the surround effects. In past times mono surround channels were used, but nowadays stereo surround channels are used for 5.1-channel systems.

Meanwhile, the subwoofer covers a low frequency region and has very little restriction on its position because directivity at low frequencies is lower than directivity at medium or high frequencies. Most subwoofers are able to replay 20 to 30 Hz but high performance subwoofers are able to replay sounds lower than 20 Hz. Such low frequency sound provides not only the sounds but also a feeling of vibration thus making a more realistic sound replay.

In some embodiments, the subwoofers have amplifiers therein. Recently, active type subwoofers having built-in amplifiers are becoming more popular for obtaining powerful sounds and automatic volume control.

The above mentioned speakers, except the subwoofer, are generally not physically different than each other but have different locations depending on their roles in the system. In some embodiments, the center speaker has slightly different characteristics for proper processing of the dialogues in a movie.

There are various types of multi-channel digital sound replay system, for example, 5.1-channel system, such as 4-channel system, 4.1-channel system, and the like. Recently, 6.1-channel surround home theater systems are being introduced. When installing a home theater having multi-channel digital sound replay system, each speaker must be connected to the corresponding terminals for signal output.

A typical wireless distribution and transmission method for a multichannel sound transmission is a time division multiple access (TDMA) method. The TDMA based multi-channel wireless speaker system illustrated in FIG. 1 adopts a method wherein each sound data is transmitted during the time slot assigned for each speaker so as to avoid inter-channel interferences.

In TDMA, M number of multichannel sound data extracted from the sound source are packetized in an appropriate time frame for outputting via wireless sound speakers (hereinafter referred to as “WSS”), then transmitted via wireless channels to corresponding speakers during the total transmission period through the modulator further adding replay time information including speaker identification, current time, replay time, and the like.

Each WSS outputs sounds through the speaker after extracting sound data by demodulating the wireless signal received. In TDMA, because multichannel sound data is continuously transmitted in temporal perspective, synchronization based on current time and replay time must be performed between the speakers after all the channel signals are received in order to replay sounds at the same time in all WSSs. For this reason, a buffer that is able to store sound data of more than two packets is required for continuous replay, and a structure for synchronization between the WSSs should be added.

For synchronization between the WSSs, current time information must be periodically transmitted from the wireless sound distributer and transmitter (hereinafter referred to as “WSDT”), and all the packets must be transmitted with replay time information. In each WSS, a reference time is set by receiving current time information and based on a reference time. Sound replay should be performed in accordance with replay time information of each packet. Such a structure requires an additional storage space, a timer, and a replay time controller because a received packet must be stored in a buffer until the replay time point. This causes an increase in hardware complexity, and it has further disadvantages in that transmission efficiency is reduced because additional information for synchronization between the speakers must be added to all the packets.

SUMMARY

Replay time difference has been a problem of a conventional TDMA based multichannel wireless speaker system. In one general aspect, there is provided a transmitter unit compensation method having simpler structure in comparison to the conventional receiver unit control method by pre-compensating for replay time difference between the speakers at the transmitter unit.

In another aspect, there is provided a method to solve the problem of the conventional TDMA based multichannel wireless speaker system that requires an additional storage space, a timer, and a replay time controller because a received packet must be stored in a buffer until the replay time point causing an increase in hardware complexity, and to overcome the disadvantage of reduced transmission efficiency because an additional information for synchronization between the speakers must be added to all the packets.

To achieve above-described objectives, a data transmission method in a TDMA based multichannel wireless transmission system of the present invention comprises the steps of: storing multiple data having identical replay time information in each corresponding memory by transmitting the data in accordance with the input clock signal; outputting sequentially and repeatedly the stored data one by one from the corresponding memory in accordance with the output clock signal; and transmitting a transmit packet modulated by the output data via corresponding wireless channel.

To achieve above-described objectives, a data transmission device in a TDMA based multichannel wireless transmission system of the present invention is comprised of: a bank comprised of multiple memories wherein multiple data having identical replay time information are received in accordance with the input clock signal and stored in the corresponding memories and the stored data are sequentially and repeatedly outputted one by one in accordance with the output clock signal; a modem for generating transmit packets modulated by the output data; and a communication unit for transmitting the modulated transmit packets via the wireless channel.

To achieve above-described objectives, a TDMA based multichannel wireless transmission system of the present invention is comprised of: a wireless sound transmitter for receiving multiple data having identical replay time information in accordance with the input clock signal, storing the data into the corresponding memories, outputting sequentially and repeatedly the stored data one at a time, and transmitting the transmit packets modulated by the output data via the corresponding transmission channel; and a plurality of wireless sound speakers for replay sounds by receiving the transmit packets from the wireless sound transmitter.

To achieve above-described objectives, a data transmission method in a TDMA based multichannel wireless transmission system of the present invention comprises the steps of: conveying multiple data having identical replay time information to the corresponding delay units; outputting data inputted to the delay unit with a predetermined time delay as assigned to each sound channel; generating transmit packets that are modulated by the output data, respectively; and transmitting the generated transmit packets according to the order of a predetermined sequence via the wireless channels.

To achieve above-described objectives, a data transmission device in a TDMA based multichannel wireless transmission system of the present invention is comprised of: a delay unit for outputting data inputted to the delay unit with a predetermined time delay as assigned to each sound channel; a modem for generating transmit packets modulated by the output data of the delay unit; and a communication unit for transmitting the modulated transmit packets via the wireless channels.

To achieve above-described objectives, the present invention suggests a TDMA based multichannel wireless transmission system comprising: a wireless sound transmitter receiving multiple data having identical replay time point, outputting the received data with a predetermined time delay as assigned to each sound channel, and transmitting the transmit packets modulated by the output data via the wireless channels; and a plurality of wireless sound speakers for replaying sounds by receiving the transmit packets from the wireless sound transmitter.

The present invention pre-compensates differences in the replay time points, occurring between the speakers in a TDMA based multichannel wireless transmission system, through the delay of the sound data in the WSDT; it enables all the WSSs to replay sounds at an identical sound replay time point without requiring an additional structure for synchronization of the WSSs so that the structure of the WSS can be simplified and therefore the system can be realized with minimum complexity.

Besides, a pre-compensation technique and device for the synchronization between the speakers of the multichannel wireless speaker system of the present invention provides high quality sounds for listeners by enhancing transmission efficiency since it does not require additional data such as present time information and replay time information.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a conventional TDMA based multichannel wireless transmission system.

FIG. 2 is a diagram illustrating the layout of 5.1-channel sound system.

FIG. 3 is a diagram illustrating the structure of the transmitter unit of a TDMA based multichannel wireless transmission system in accordance with an exemplary embodiment of the present invention.

FIG. 4 is a diagram illustrating the structure of the receiver unit of a TDMA based multichannel wireless transmission system in accordance with an exemplary embodiment of the present invention.

FIG. 5 is a diagram illustrating the FIFO bank structure of the transmitter unit of a TDMA based multichannel wireless transmission system in accordance with an exemplary embodiment of the present invention.

FIG. 6 is a diagram illustrating the FIFO bank structure of the transmitter unit of a TDMA based multichannel wireless transmission system in accordance with an exemplary embodiment of the present invention.

FIG. 7 is a diagram illustrating a transmission structure of a TDMA based multichannel wireless transmission system in accordance with an exemplary embodiment of the present invention.

FIG. 8 is a diagram illustrating the structure of the receiver unit of a TDMA based multichannel wireless transmission system in accordance with an exemplary embodiment of the present invention.

Throughout the drawings and the description, unless otherwise described, the same drawing reference numerals should be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience.

DESCRIPTION

The following description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein may be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness.

TDMA based present invention suggests a transmission method wherein M number of sound data are acquired and stored simultaneously in each corresponding sound buffer, and the stored sound data is sequentially transmitted in accordance with time slots correspondingly assigned to each sound data, and the time differences occurring at this time are compensated for at the wireless sound distributer and transmitter (WSDT).

FIG. 2 illustrates a speaker layout of a conventional 5.1-channel sound system.

In this example, the 5.1-channel sound system is comprised of a left stereo channel 110, a right stereo channel 120, a left surround channel 130, a right surround channel 140, a center channel 150, and a low frequency enhancement channel (LFE) 160.

FIG. 3 illustrates a transmission structure of a WSDT in accordance with an example of the present invention. Hereinafter, a transmission structure of a WSDT in accordance with an exemplary embodiment of the present invention will be described with reference to FIG. 3.

As shown in FIG. 3, M number of multichannel sound acquired from the sound source are packetized with an appropriate time frame (N) for replay by the WSSs. The resulting packets are modulated for wireless transmission, and a transmit packet (hereinafter referred to as “Tx packet”) is obtained thereafter.

Time duration for transmission of a Tx packet is T. In a multichannel wireless speaker system having M number of sound channels, the time duration for complete wireless data transmission of all the sound channels (M×T) must be less than the sound data replay time (N) for a real-time transmission of the sound data. Therefore it is assumed that any wireless transmission modem that is being used in the present invention satisfies such condition.

As shown in FIG. 3, in a TDMA based WSDT, data streams are transmitted in ascending order such as data stream of the sound channel 1, data stream of the sound channel 2, and the like. Once the data stream of the sound channel M is finally transmitted in accordance with the above-described manner, the WSDT begins to transmit the data stream of the sound channel 1.

According to FIG. 3, a WSDT divides data streams of the sound channels 1 to M into data packets having an allowable size for transmission. The WSDT transmits first data packet divided from data stream of the sound channel 1. The WSDT generates first data packet divided from data stream of the sound channel 2 through the process described as follows.

The WSDT discards part of data stream of the sound channel 2 corresponding to time T that is required for transmission of the first data packet of the sound channel 1, and generates first data packet of the sound channel 2 using the remaining part of data stream of the sound channel 2. The length of the data packet for the sound channel 2 transmitted via the wireless channel is that of data packet for the sound channel 1 transmitted via the wireless channel. In other words, if the replay time required for the data packet of the sound channel 1 is N, the replay time required for the data packet of the sound channel 2 is N as well.

As shown in FIG. 3, the WSDT generates a Tx packet transmittable for a duration T through the modulation of the data packet having replay time N. The WSDT generates a first data packet divided from data stream of the sound channel M through the process described as follows. The WSDT discards part of data stream of the sound channel M corresponding to time T(M−1) that is required for transmission of the first data packet of the sound channel 1 to the first data packet of the sound channel (M−1), and generates first data packet using the remaining part of data stream of the sound channel M.

The length of the data packet for the sound channel M transmitted via the wireless channel is identical to that of data packet for the sound channel 1 transmitted via the wireless channel. In other words, if the replay time required for the data packet of the sound channel 1 is N, the replay time required for the data packet of the sound channel M is N as well.

FIG. 4 illustrates a packet receiving process by the WSSs in accordance with an example of the present invention. Hereinafter, a packet receiving process by the WSSs in accordance with an example of the present invention will be described with reference to FIG. 4.

As shown in FIG. 4, when all the sound channel data is transmitted via the wireless channel and is extracted at each WSS through demodulation of the received packets (hereinafter referred to as “Rx packet”) corresponding to their own time slots. When all the Rx packets are received, the received data is replayed instantly.

The first WSS receives Tx packets that are divided from the first data stream while the second WSS receives Tx packets that are divided from the second data stream. The M-th WSS receives Tx packets that are divided from the M-th data stream.

The first WSS demodulates Tx packets into data packets through the demodulation unit 400 when the first Tx packet is completely received. The first WSS immediately starts to replay after demodulation of the received Tx packet. The data of the second sound channel is received by the second WSS with a time delay T while the sound data of the first sound channel is being replayed.

The second WSS demodulates Tx packets into data packets through the demodulation unit 402 when the first Tx packet is completely received. The second WSS immediately starts to replay after demodulation of the received Tx packet. The sound data replayed by the second WSS has a time delay T with respect to the sound data replayed by the first WSS. But because the sound data has been transmitted with a time delay T from the WSDT, sounds replayed by the two WSSs have identical replay time point.

In a similar manner as described above, the data of the M-th sound channel is received by the M-th WSS with a time delay (M−1)T while the sound data of the first sound channel is being replayed. The M-th WSS demodulates Tx packets into data packets through the demodulation unit 404 when the first Tx packet is completely received. The M-th WSS immediately starts to replay after demodulation of the received Tx packet. The sound data replayed by the M-th WSS has a time delay (M−1)T with respect to the sound data replayed by the first WSS. But because the sound data has been transmitted with a time delay (M−1)T from the WSDT, sounds replayed by the two WSSs have identical replay time point.

In other words, although at first WSSs start to replay sounds according to the preset operation sequence assigned to each WSS, when sound data replay of all M number of sound channels begins to start, sounds having identical replay time point are simultaneously being replayed in realtime from all the speakers.

FIG. 5 illustrates the structure of a WSDT in accordance with an example of the present invention. Hereinafter, a WSDT in accordance with an exemplary embodiment of the present invention will be described with reference to FIG. 5.

A WSDT shown in FIG. 5 is comprised of a first-in first-out (hereinafter referred to as “FIFO”) bank 500, a multiplexer unit (hereinafter referred to as “MUX”) 504, a sound channel selection unit 502, a modem (i.e. modulation unit) 506, and an antenna 508. A WSDT may further comprise other elements including the above-described elements.

The FIFO bank 500 has a length of N and receives data streams that are to be transmitted to the sound channels 1 to M. The FIFO bank 500 also receives input clock (in_clk), output clock (out_clk), and sound channel selection signal (CS). The FIFO bank 500 outputs one data stream selected among the data streams of the sound channels 1 to M that are inputted according to the received sound channel selection signal. The FIFO bank 500 divides received data streams into data packets having the same unit size before sending out the received data streams.

The MUX 504 sends a data stream selected among the data streams of the sound channels 1 to M that are received from the FIFO bank 500 to the modem 506. The modem 506 generates Tx packets by modulating the data packets received from the MUX, and transmits Tx packets outside via the antenna 508. The sound channel selection unit 502 generates a command signal (i.e. CS) directing sequential selection among the data streams that are to be transmitted to the sound channels 1 to M, for every preset time interval (T) one at a time.

FIG. 6 illustrates an example of the FIFO bank 500 in accordance with an example of the present invention. Hereinafter, the structure and the operation of the FIFO bank 500 will be described with reference to FIG. 6. As shown in FIG. 6, the FIFO bank 500 is comprised of M number of FIFOs 600 to 604.

When power is applied to the WSDT, sound data is inputted to the FIFO bank 500 using the same input clock. The input clock for the sound data must be equally set as the sampling clock for the sound data. As described above, the FIFO bank 500 is comprised of M number of FIFOs.

Storage space of each FIFO is equal to the length of the sound data that is outputted during the duration of one output clock. Because data is simultaneously inputted to each FIFO using the same input clock, the time to store input data of length N is equal for all data inputs. When a data of length N is inputted to a FIFO, sound data is transmitted according to the process sequence described hereinafter. Inputting to the FIFO is continued even when the next operation sequence is being performed. If the FIFO already had stored N number of data, then the earliest input data in the FIFO is discarded first whenever a consecutive data is inputted so that the FIFO always maintains data no more than an amount N.

1. The sound channel selection unit selects a data FIFO to which data is transmitted during the first time slot.

2. The selected FIFO outputs N number of data according to the output clock generated by the modem. Because in general input clock frequency for a sound data is much lower than the operating speed of the modem, the output clock frequency is much higher than that of the input clock frequency. At this step, if the number of stored data in the selected FIFO is less than N, the FIFO waits until the number of stored data reaches N before outputting the stored data.

3. N number of data outputs are transmitted to the WSSs through the modem via wireless channels.

4. The WSS allocated with a time slot at present replays sound without delay after extraction of the sound from the received wireless signal.

5. After N number of sound data of the FIFO selected at present are transmitted, a sound data FIFO to be used during the next time slot is selected and the above-described process is repeated from the step 2.

For example, if the output signal of the sound channel selection unit is for the sound channel 1, the FIFO bank outputs corresponding sound data assigned to the sound channel 1 that is stored in the FIFO 600 in accordance with the output clock. The sound data stored in the FIFO 600 corresponding to the sound channel 1 is transmitted through a modulation process via the antenna. During the time that the stored data in the FIFO 600 corresponding to the sound channel 1 is being transmitted, the FIFO bank 500 receives sound data according to the input clock. At this time, because a bank of the FIFO 600 corresponding to the sound channel 1 is empty, the received sound data is sequentially stored. But there is no available storage in the FIFO 602 to FIFO 604 corresponding to the sound channels 2 to M respectively. Therefore, the sound data in the FIFOs 602, 604 corresponding to the sound channel 2 and the sound channel M are discarded in descending order of stored time, and the amount of the data to be discarded is equal to the size of the newly inputted sound data.

After sending the sound data corresponding to the sound channel 1, the sound channel selection unit generates (outputs) a signal for selection of the sound channel 2. The FIFO bank outputs corresponding sound data assigned to the sound channel 2 that is stored in the FIFO 602 in accordance with the output clock. The sound data stored in the FIFO 602 corresponding to the sound channel 2 is transmitted through a modulation process via the antenna. During the time that the stored data in the FIFO 602 corresponding to the sound channel 2 is transmitted, the FIFO bank 500 receives sound data according to the input clock. At this time, because a bank of the FIFO 600 corresponding to the sound channel 1 and the FIFO 602 corresponding to the sound channel 2 are not full, the received sound data is sequentially stored. But there is no available storage in the FIFO 604 corresponding to the sound channels 3 to M. Therefore, the sound data in the FIFOs corresponding to sound channels 3 to M are discarded in descending order of stored time, and the amount of the data to be discarded is equal to the size of the newly inputted sound data. By repeating above-described process, the FIFO bank sends out sound data sequentially by using data inputs from the sound channels 1 to M. Thereafter, starting from the second data packets of each sound channel, all the input data packets are transmitted to the MUX without discarding any data in the FIFO bank as described above.

Although at first WSSs start to replay sounds according to the preset operation sequence assigned to each WSS, when sound replay starts from all the speakers, sounds are replayed at the identical replay time point due to the synchronization between the speakers. Because each WSS immediately replays sounds by extracting sounds from the received data during its own time slot, additional structure or devices are not necessary for handling information such as present time and replay time point for synchronization of the WSSs therefore the structure of the WSS can be significantly simplified by eliminating sound data buffer required for synchronization.

FIG. 7 illustrates a transmission structure of a WSDT in accordance with an example of the present invention. Hereinafter, a transmission structure of a WSDT in accordance with an example of the present invention will be described with reference to FIG. 7.

As shown in FIG. 7, M number of multichannel sound acquired from the sound source are packetized into a time frame (N) for replay by the WSSs. The resulting packets are modulated for wireless transmission, and a Tx packet is obtained thereafter. Time required for transmission of a Tx packet is T. In a multichannel wireless speaker systems having M number of sound channels, because the time required for complete wireless data transmission of all the sound channels (M×T) must be less than the sound data replay time (N) for a real-time transmission of the sound data, it should be assumed that any wireless transmission modem that is being used in the present invention satisfies such condition.

According to FIG. 7, data streams of the sound channel 1 to M are transmitted to a delay block 700. In a TDMA based WSDT, data streams are transmitted sequentially starting from the data stream of the sound channel 1 followed by the data stream of the sound channel 2, and so on. Once the data stream of the sound channel M is finally transmitted in accordance with the above-described manner, the WSDT begins to transmit the data stream of the sound channel 1.

When the data streams of the sound channels 1 to M are simultaneously inputted, the delay block 700 transmits the data stream of the sound channel 1 with a preset time delay according to the control signal of the controller (not shown here). As described above, the delay time of the data stream in the delay block 700 is related to the number of data streams and required time for transmitting one packet among the packets that are formed by dividing the data stream into multiple packets of a predetermined size.

Delay lengths for data streams of assigned sound channels in the delay block are different from each other. Delay unit 1 of the delay block outputs data stream of the sound channel 1 with a time delay of (M−1)×T. Delay unit 2 of the delay block outputs data stream of the sound channel 2 with a time delay of (M−2)×T. The last data stream of the sound channel M is directly outputted without any delay.

The delay block may be implemented by using a buffer circuit (hereinafter referred to as “buffer”). The size of the buffer can be adjusted to be matched with the length of delay. Whenever data streams are inputted to the buffer, delayed data packets are outputted. If the length of the input data stream is shorter than the length of delay, delayed data packets are outputted after inserting null data.

In FIG. 7, data streams of sound channels 1 to M outputted from the delay block are illustrated. The WSDT divides data streams of sound channels 1 to M outputted from the delay block into data packets having an allowable size for transmission. The WSDT divides a data stream into packets of size N as shown in FIG. 7. The size of the packets formed by dividing the data streams in the WSDT may vary depending on the user capacity of the system or WSS specifications.

The WSDT transmits the first data packet of the sound channel 1 within time T followed by transmission of the first data packet of the sound channel 2 within time T. By repeating above-described process, the WSDT finally transmits the first data packet of the sound channel M. Subsequently, the WSDT starts to transmit the second data packet of the sound channel 1. As shown in FIG. 7, although at times of initial transmission null data are included in all sound channels except the sound channel M, but only sound data are transmitted starting from the second transmission.

As shown in FIG. 7, WSDT generates Tx packets that can be transmitted within time T through modulation of data packets having replay time N. In other words, data packets are transformed into the Tx packets through modulation process in the modulation unit which is not shown in FIG. 7.

FIG. 8 illustrates a packet receiving process by the WSSs in accordance with an example of the present invention. Hereinafter, a packet receiving process by the WSSs in accordance with an exemplary embodiment of the present invention will be described with reference to FIG. 8.

As shown in FIG. 8, when all the sound channel data is transmitted via the wireless channel, transmission data packets are generated at each WSS through demodulation of the received Tx packets corresponding to their own time slots. When all the Tx packets are received, sound data are replayed using the data packets generated through the demodulation process.

The first WSS 800 receives Tx packets divided from the first sound data stream while the second WSS 802 receives Tx packets divided from the second sound data stream. The M-th WSS 804 receives Tx packets divided from the M-th sound data stream.

The first WSS 800 immediately starts to replay after demodulation of the received Tx packet when the first Tx packet is completely received. At the very first moment, actual sound is not outputted from the speaker even though immediate replay process has been started because the front part of the first packet contains null data. In other words, because the WSS 800 starts to replay after the time T required to receive packets and the time (M−1)×T delayed by the WSDT, therefore the actual sound replay starts after the total time delay of M×T.

The second WSS 802 immediately starts to replay after demodulation of the received Tx packet when the first Tx packet is completely received. At the very first moment, actual sound is not outputted from the speaker even though immediate replay process has been started because the front part of the first packet contains null data. As described above the WSDT transmits the first Tx packet of the sound channel 1 from time 0 to time T, and transmits the first Tx packet of the sound channel 2 from time T to time 2T. In other words, because the WSS 802 starts to replay after the time 2T required to receive packets and the time (M−2)×T delayed by the WSDT, the actual sound replay starts after the total time delay of M×T.

The M-th WSS 804 immediately starts to replay after demodulation of the received Tx packet when the first Tx packet is completely received. From the very first moment, actual sound is outputted from the speaker as immediate replay process is started because the front part of the first packet does not contain null data unlike other sound channels. In other words, because the WSS 804 does not have other delay time except time M×T required to receive Tx packets, actual sound is outputted from the speaker after a time delay of M×T. Hence, all the WSSs start actual replay after the same time delay of M×T, and therefore no additional operation is required for synchronization between the WSSs. It is assumed that all the WSSs have identical hardware configuration.

Each WSS immediately replays by extracting sounds from the received data corresponding to its own time slot, therefore additional structure or devices are not necessary for handling information such as present time and a replay time point for synchronization of the WSSs. In other words, a multichannel sound system of the present invention enables an efficient sound data transmission, and has an advantage that it does not require a buffer to store received sound data for synchronization.

A number of examples have been described above. Nevertheless, it should be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims. 

1. A data transmission method in a TDMA based multichannel wireless transmission system, the method comprising: storing multiple data having identical replay time information in each corresponding memory by transmitting the data in accordance with the input clock signal; outputting sequentially and repeatedly the stored data one by one from the corresponding memory in accordance with the output clock signal; and transmitting a transmit packet modulated by the output data via a corresponding wireless channel.
 2. The method of claim 1, wherein the time required for transmitting sequentially one set of the transmit packets of all the sound channels is less than or equal to the replay time of the stored data in the memory.
 3. The method of claim 1, wherein the memory discards the oldest stored data therein when a data is inputted in accordance with the input clock signal after all the storage spaces of the memory are occupied by data.
 4. The method of claim 3, wherein if the time required for transmitting one transmit packet through the wireless channel is T, the replay time of a discarded data in the M-th memory is (M−1)T.
 5. The method of claim 4, wherein the stored data in the memory are discarded only at time point prior to the transmission of the first transmit packet in the corresponding sound channels thereof.
 6. A data transmission device in a TDMA based multichannel wireless transmission system, the device comprising: a bank comprised of multiple memories wherein multiple data having identical replay time information are received in accordance with the input clock signal and stored in the corresponding memories, and the stored data is sequentially and repeatedly outputted one by one in accordance with the output clock signal; a modem for generating transmit packets modulated by the output data; and a communication unit for transmitting the modulated transmit packets via corresponding wireless channel.
 7. The device of claim 6, further comprising a sound channel selection unit that transmits a sound channel selection signal to the bank, wherein the sound channel selection signal enables the stored data being outputted sequentially and repeatedly from the memory one at a time.
 8. The device of claim 6, wherein the memory discards the oldest stored data therein when a data is inputted in accordance with the input clock signal after all the storage spaces of the memory are occupied by data.
 9. The device of claim 8, wherein if the time required for transmitting one transmit packet through the wireless channel is T, the replay time of a discarded data in the M-th memory is (M−1)T.
 10. A TDMA based multichannel wireless transmission system comprising: a wireless sound transmitter receiving multiple data having identical replay time information in accordance with the input clock signal, storing the data into the corresponding memories, outputting sequentially and repeatedly the stored data one at a time, and transmitting the transmit packets modulated by the output data via the wireless channel; and a plurality of wireless sound speakers for replaying sounds by receiving the transmit packets from the wireless sound transmitter.
 11. The TDMA based multichannel wireless transmission system according to claim 10, wherein the wireless sound transmitter comprises: a bank comprised of multiple memories wherein multiple data having identical replay time information is received in accordance with the input clock signal and stored in the corresponding memories and the stored data is sequentially and repeatedly outputted one by one in accordance with the output clock signal; a modem for generating transmit packets modulated by the output data; and a communication unit for transmitting the modulated transmit packets via the wireless channel.
 12. The TDMA based multichannel wireless transmission system according to claim 11, wherein the memories discard the oldest stored data therein when a data is inputted in accordance with the input clock signal after all the storage spaces of the memories are occupied by data.
 13. The TDMA based multichannel wireless transmission system according to claim 12, wherein if the time required for transmitting one transmit packet through the wireless channel is T, the replay time of a discarded data in the M-th memory is (M−1)T.
 14. A data transmission method in a TDMA based multichannel wireless transmission system, the method comprising: conveying multiple data having identical replay time information to the corresponding delay units; outputting data inputted to the delay unit with a predetermined time delay as assigned to each sound channel; generating transmit packets that are modulated by the output data, respectively; and transmitting the generated transmit packets according to the order of a predetermined sequence via the wireless channels.
 15. The method of claim 14, wherein if the number of sound channels is M and the time required for transmitting one transmit packet through the wireless channel is T, the length of data delay corresponding to k-th sound channel is (M−k)T.
 16. The method of claim 15, wherein the data delay is performed only at a time point prior to the transmission of the first transmit packet in the corresponding sound channels thereof.
 17. The method of claim 14, wherein the time required for transmitting sequentially one set of the transmit packets of all the sound channels is less than or equal to the replay time of the demodulated transmit packets.
 18. A data transmission device in a TDMA based multichannel wireless transmission system, the device comprising: a delay unit for outputting data inputted to the delay unit with a predetermined time delay as assigned to each sound channel; a modem for generating transmit packets modulated by the output data of the delay unit; and a communication unit for transmitting the modulated transmit packets via the wireless channels according to the predetermined transmission order.
 19. The device of claim 18, wherein if the number of sound channels is M and the time required for transmitting one transmit packet through the wireless channel is T, the length of data delay corresponding to k-th sound channel is (M−k)T.
 20. A TDMA based multichannel wireless transmission system comprising: a wireless sound transmitter for receiving multiple data having identical replay time point, outputting the received data with a predetermined time delay as assigned to each sound channel, and transmitting the transmit packets modulated by the output data via the wireless channels; and at least one wireless sound speaker for replaying sounds using the received transmit packets from the wireless sound transmitter.
 21. The TDMA based multichannel wireless transmission system according to claim 20, wherein the wireless sound transmitter comprises: a delay unit for outputting data inputted to the delay unit with a predetermined time delay as assigned to each sound channel; a modem for generating transmit packets modulated by the output data of the delay unit; and a communication unit for transmitting the modulated transmit packets via the wireless channels.
 22. The TDMA based multichannel wireless transmission system according to claim 21, wherein if the number of sound channels is M and the time required for transmitting one transmit packet through the wireless channel is T, the length of data delay corresponding to k-th sound channel is (M−k)T. 